This invention pertains to lighting sources, in general, and to a lighting source that utilizes Light Emitting Diodes (LED""s), in particular
LED""s have many advantages as light sources. However, in the past LED""s have found application only as specialized light sources such as for vehicle brake lights, and other vehicle related lighting, and recently as flashlights. In these prior applications, the LED""s are typically mounted in a planar fashion in a single plane that is disposed so as to be perpendicular to the viewing area. Typically the LED planar array is not used to provide illumination, but to provide signaling.
Recent attempts to provide LED light sources as sources of illumination have been few, and generally unsatisfactory from a general lighting standpoint.
It is highly desirable to provide a light source utilizing LED""s that provides sufficient light output so as to be used as a general lighting source rather than as a signaling source.
One problem that has limited the use of LED""s to specialty signaling and limited general illumination sources is that LED""s typically generate significant amounts of heat. The heat is such that unless the heat is dissipated, the LED internal temperature will rise causing degradation or destruction of the LED.
It is therefore further desirable to provide an LED light source that efficiently conducts heat away from the LED""s.
In accordance with the principles of the invention, an improved light source is provided. The light source includes an elongate thermally conductive member having an outer surface. A plurality of light emitting diodes is carried on the elongate member outer surface. At least some of the light emitting diodes are disposed in a first plane and others of said light emitting diodes are disposed in a second plane not coextensive with the first plane. Electrical conductors are carried by the elongate thermally conductive member and are connected to the plurality of light emitting diodes to supply electrical power thereto. The elongate thermally conductive member conducts heat away from the light emitting diodes to a thermally conductive fluid medium. A cooling device is utilized to remove heat from the light emitting diodes. In one aspect of the invention, the cooling device comprises a fluid moving device utilized to cause the fluid medium to flow to cause cooling of the elongate thermally conductive member and therefore to dissipate heat from the light emitting diodes. In another aspect of the invention, the cooling device may be an electronic or solid state device such as a Piezoelectric device or a device that uses the Peltier effect, known as a Peltier device.
In accordance with the principles of the invention, a temperature sensor is provided to determine the temperature of the light emitting diodes. The temperature sensor is coupled to a controller that monitors the temperature and controls the cooling device to vary the degree of cooling in accordance with the monitored temperature. In addition, the controller can be used to control the power provided to the light emitting diodes in response to the monitored temperature. Still further, the controller may be operated to control the light output provided by the light emitting diodes.
In the illustrative embodiment of the invention, the fluid medium is air and the fluid moving device is an air moving device.
In accordance with one aspect of the invention, an illustrative embodiment of the invention utilizes light emitting diodes that emit white light. However, other embodiments of the invention may utilize light emitting diodes that are of different colors to produce monochromatic light or the colors may be chosen to produce white light or other colors.
In accordance with another aspect of the invention the elongate thermally conductive member transfers heat from the light emitting diodes to a medium within said elongate thermally conductive member. In the illustrative embodiment of the invention, the medium is air.
In accordance with another aspect of the invention, the elongate thermally conductive member has one or more projections or fins to enhance heat transfer to the medium. The projections or fins may be disposed on the outer surface or inner surface of the elongate thermally conductive member or may be disposed on both the outer and inner surfaces.
In accordance with another aspect of the invention the elongate thermally conductive member comprises a tube. In one embodiment of the invention, the tube has a cross-section in the shape of a polygon. In another embodiment of the invention, the tube has a cross-section having flat portions.
In accordance with another embodiment of the invention, the elongate thermally conductive member comprises a channel.
In accordance with the principles of the invention, the elongate thermally conductive member may comprise an extrusion, and the extrusion can be highly thermally conductive material such as aluminum.
In one preferred embodiment of the invention the elongate thermally conductive member is a tubular member. The tubular member has a polygon cross-section. However, other embodiments my have a tubular member of triangular cross-section.
In one embodiment of the invention, a flexible circuit is carried on a surface of said elongate thermally conductive member; the flexible circuit includes the electrical conductors.
In another aspect of the invention, the flexible circuit comprises a plurality of apertures for receiving said plurality of light emitting diodes. Each of the light emitting diodes is disposed in a corresponding one of the apertures and affixed in thermally conductive contact with said elongate thermally conductive member.
The elongate thermally conductive member includes a thermal transfer media disposed therein in a flow channel.
At least one clip for mounting the elongate thermally conductive member in a fixture may be included.